In various embodiments, an image sensor and method of using an image sensor are described. In an example embodiment, the image sensor comprises a semiconductor substrate and a plurality of pixel regions with each pixel region comprising an optically sensitive material over the substrate and positioned to receive light. There is a bias electrode for each pixel region, with the bias electrode configured to provide a bias voltage to the optically sensitive material of the respective pixel region. Also included is a pixel circuit for each pixel region with each pixel circuit comprising a charge store formed on the semiconductor substrate and a read out circuit, the charge store being in electrical communication with the optically sensitive material of the respective pixel region. The pixel circuit is configured to reset the voltage on the charge store to a reset voltage during a reset period, to integrate charge from the optically sensitive material to the charge store during an integration period, and to read out a signal from the charge store during a read out period. The pixel circuit includes a reference voltage node to be coupled to the charge store during the reset period and the read out circuit during the read out period where a reference voltage is applied to the reference voltage node and is configured to be varied during the operation of the pixel circuit.